Engineer Information Communications key terms

The ratio of usable signal power to unwanted noise power at a given point in a system, usually expressed in decibels. Higher SNR means clearer reception and fewer bit errors.

The fraction of transmitted bits that are received incorrectly over a measurement interval. It quantifies link quality and depends on SNR, modulation scheme, and coding.

The theoretical maximum error-free data rate of a channel with given bandwidth and SNR, given by C = B log2(1 + SNR). It sets an upper bound no practical system can exceed.

The process of varying a carrier property such as amplitude, phase, or frequency to carry information. It maps digital bits onto waveforms suited to the transmission medium.

A modulation family that encodes bits in combined amplitude and phase states of two quadrature carriers. Higher orders such as 256-QAM carry more bits per symbol but need better SNR.

A multicarrier technique that splits data across many closely spaced orthogonal subcarriers, each modulated at low rate. It resists multipath and is used in LTE, Wi-Fi, and DSL.

A copy of the tail of an OFDM symbol appended to its front. It absorbs multipath delay spread so that inter-symbol interference is avoided after cyclic convolution with the channel.

A bandlimited signal can be reconstructed exactly if sampled at more than twice its highest frequency. Undersampling causes aliasing that cannot be removed later.

Mapping a continuous range of sample values to a finite set of discrete levels. It introduces quantization noise, which sets the achievable signal-to-noise ratio in digital conversion.

A digital encoding method that samples an analog signal at a fixed rate, quantizes each sample, and transmits the resulting binary code words. It is the basis of digital telephony.

A seven-layer framework describing network functions from physical transmission up to applications. Each layer offers services to the layer above and uses services from the layer below.

The process where each protocol layer adds its own header or trailer to data received from the layer above. The receiver strips headers in reverse order to recover the payload.

A connection-oriented transport protocol providing reliable, ordered byte streams through sequence numbers, acknowledgments, and retransmission. It also performs flow and congestion control.

A connectionless transport protocol that sends datagrams without delivery guarantees, ordering, or congestion control. Its low overhead suits real-time and query-response traffic.

The TCP connection setup exchange of SYN, SYN-ACK, and ACK that synchronizes initial sequence numbers and confirms both endpoints can send and receive.

An addressing scheme using variable-length prefixes written as an address plus slash length. It replaced fixed address classes and enables efficient route aggregation.

A bit pattern that separates the network portion from the host portion of an IP address. It determines which destinations are local and how addresses are grouped into subnets.

A link-state interior gateway protocol where routers flood link information and each computes shortest paths using Dijkstra's algorithm. It supports hierarchical areas to limit flooding.

The path-vector protocol that exchanges reachability between autonomous systems on the Internet. Route selection uses attributes such as AS path length and local preference.

The largest payload a link can carry in one frame. Packets larger than the path MTU must be fragmented or dropped, so path MTU discovery avoids silent failures.

The procedure that transfers an ongoing connection from one base station or cell to another as a mobile terminal moves. It must minimize interruption and call drop risk.

A radio technique using multiple transmit and receive antennas to improve capacity and reliability through spatial multiplexing or diversity. It is central to LTE, 5G, and Wi-Fi.

Directing radio energy toward intended users by adjusting the phase and amplitude of signals across an antenna array. It improves coverage and reduces interference.

Dividing a cell into angular sectors served by directional antennas to increase capacity and reduce interference. It is often described by the number of sectors per site.

Variation in received signal strength caused by multipath propagation, shadowing, or movement. Fast fading from multipath requires diversity or equalization to mitigate.

Carrying multiple optical channels on a single fiber by assigning each a distinct wavelength. Dense WDM greatly increases capacity without additional fiber.

A device, commonly erbium-doped fiber, that boosts optical signals directly without converting them to electrical form. It amplifies all wavelengths simultaneously but adds noise.

Spreading of optical pulses as different wavelength components or modes travel at different speeds. It limits reach and bit rate unless compensated or managed.

Adding redundant bits so the receiver can detect and correct some transmission errors without retransmission. It improves effective reach and lowers required signal power.

Symmetric encryption uses one shared secret key for both directions, while asymmetric encryption uses a public key to encrypt and a private key to decrypt. Each trades speed against key distribution.

A value computed from a message and a private key that anyone can verify with the corresponding public key. It provides integrity, authenticity, and non-repudiation.

A one-way function mapping arbitrary input to a fixed-length digest. Cryptographic hashes must resist preimage, second-preimage, and collision attacks.

The policies, software, and certificate authorities that issue and revoke digital certificates binding public keys to identities. It underpins trust in TLS and signed email.

A protocol that establishes an authenticated, encrypted channel between client and server using certificates and negotiated session keys. It protects web, mail, and API traffic.

A stack is a last-in-first-out collection with push and pop, while a queue is first-in-first-out with enqueue and dequeue. Both are fundamental abstract data types.

A measure of how running time or memory grows with input size, usually expressed in big-O notation. It predicts scalability independent of hardware.

Japanese legislation governing radio station licensing, frequency assignment, and radio equipment standards, administered by the Ministry of Internal Affairs and Communications. It underpins legal operation of wireless systems.

The international treaty text allocating radio frequency bands to services and setting coordination rules among administrations. It forms the basis for national spectrum regulation.

Japanese law regulating telecommunications carriers, requiring registration or notification and imposing obligations on dominant carriers. It also governs interconnection and universal service.